Add loopback support to WASAPI

[MarcusTomlinson]

This change allows WASAPI users to capture "loopback" streams from render devices.

[MatzeOGH]

I had to define an output stream parameters before getting it to work.
Is that intended behavior?

[MarcusTomlinson]

Oh interesting, nah, I’d say that’s a bug.

I had just been testing it with both input and output parameters configured so didn’t pick it up.

I’ll look into it later this week. For now you’ll just have to workaround it the way you are.

Thanks for pointing this out.